Renewable energy systems are becoming more prevalent due to their advantages over the conventional fossil-based power generation systems. By harvesting energy from renewable energy sources, the detrimental impact of the conventional fossil-based power generation systems can significantly be reduced. In order to bring renewable energy systems into mainstream power generation, the efficiency of the renewable energy system should be sufficiently high under different conditions. One of the challenges is the erratic nature of renewable energy systems. For instance, in the case of solar based power generation systems, solar irradiance varies randomly depending on the weather condition. Similarly, in the case of wind based power generation systems, the speed of the wind turbine can significantly fluctuate based on weather conditions. Preferably, power converters used to extract power from renewable energy sources should be able to efficiently extract power under a wide range of operating conditions.
Photovoltaic (PV) panels are commonly used to convert solar energy to electricity. These panels are connected to a solar power conditioning system which extracts the electricity and feeds it to the grid and/or to local loads. Micro-inverters are widely used as the power conditioning system for a PV panel. Micro-inverters have several advantages such as allowing for individual maximum power point tracking (MPPT) and eliminating partial shading problem. FIG. 1 shows a typical power conditioning system for a PV micro-inverter. According to FIG. 1, the micro-inverter power conditioning system includes two stages: a DC/DC converter and a DC/AC inverter. The DC/DC converter is responsible for boosting the voltage, tracking the maximum power point of the PV panel, and possibly providing galvanic isolation. The DC/AC inverter is responsible for injecting a high quality current to the utility grid. In addition to these components, there is also a control system that controls the DC/DC converter and the DC/AC inverter to thereby enable the PV micro-inverter to perform these tasks. As well as these components, there is also a communication system which interacts with the control system to monitor and interact with any externally controlled settings.
Referring to FIG. 2, illustrated is an exemplary detailed block diagram of a control system for a micro-inverter according to the prior art. As can be seen from FIG. 2, the DC/DC converter and the DC/AC inverter have independent controllers. The controller for the DC/DC converter determines the gate pulses for the DC/DC converter in order to track the maximum power point of the PV panel. The controller for the DC/AC inverter has two cascaded control loops. The external loop regulates the DC-bus voltage by adjusting the reference value of the output current in order to guarantee the power balance. The current loop controls the output current of the inverter to allow for the injection of a nearly sinusoidal current into the utility grid.
One of the main challenges in the micro-inverter is how to maintain a high efficiency for a very wide range of operating conditions. For example, the PV panel output voltage can vary significantly based on the temperature and the irradiance (e.g., for a typical currently produced 60-cell PV panel, the voltage can vary between 19V-50V). One of the difficulties for the control system is that of controlling the converter in order to achieve high efficiency despite the extremely high variations of the operating points.
Based on the above, there is therefore a need for systems and devices which mitigate if not avoid the shortcomings of the prior art.